package com.jml.juc;


import java.util.ArrayList;
import java.util.concurrent.ExecutionException;
import java.util.concurrent.ForkJoinPool;
import java.util.concurrent.ForkJoinTask;
import java.util.concurrent.RecursiveTask;

/**
 *
 */

public class ForkJoinTaskDemo extends RecursiveTask<Long> {

    private static final int THRESHOLD = 10000;
    private long start;
    private long end;

    public ForkJoinTaskDemo(long start, long end) {
        this.start = start;
        this.end = end;
    }

    @Override
    public Long compute() {
        long sum = 0;
        boolean canCompute = (end - start) < THRESHOLD;
        if (canCompute) {
            for (long i = start; i <= end;i++) {
                sum += i;
            }
        } else {
            //分成100个小任务
            long step = (start + end) / 100;
            ArrayList<ForkJoinTaskDemo> list = new ArrayList();
            long pos = start;
            for (int i = 0; i < 100; i++) {
                long lastOne = pos + step;
                if (lastOne > end) {
                    lastOne = end;
                }
                ForkJoinTaskDemo subTask = new ForkJoinTaskDemo(pos, lastOne);
                pos = pos + step + 1;
                list.add(subTask);
                subTask.fork();
            }
            for (ForkJoinTaskDemo t : list) {
                Long joinResult = t.join();
                System.out.println(joinResult);
                sum = sum + joinResult;
            }
        }
        return sum;
    }

    public static void main(String[] args) {
        ForkJoinPool forkJoinPool = new ForkJoinPool();
        ForkJoinTaskDemo task = new ForkJoinTaskDemo(0, 200000L);
        ForkJoinTask<Long> result = forkJoinPool.submit(task);
        try {
            long res = result.get();
            System.out.println("sum=" + res);
        } catch (InterruptedException e) {
            e.printStackTrace();
        } catch (ExecutionException e) {
            e.printStackTrace();
        }
    }
}

